Downhole systems are used when performing an operation downhole such as drilling a well in the subterranean formation, cleaning a well, etc. Downhole systems are built from several tools specific for the operation to be performed. Even though the downhole system is built for a specific operation, some of the tools can be reused for another operation.
One downhole system is a drilling system comprising a drilling tool with a drilling head and a motor for driving the drilling tool. If the drilling head gets stuck while drilling, the drilling head may be destroyed; however, the rest of the system may still be intact and can thus be reused, unless it has been stuck together with the drilling head.
For solving this problem, several release devices have been made so that the drilling head can be released from the rest of the system when the drilling head gets stuck during drilling. The drilling head is released when a signal is sent from a control unit above surface to a power unit in the system, the power unit subsequently pressing a fluid into the release device wherein the pressurised fluid is used for a mechanical release of the drilling head.
In the event that the communication from above surface to the system has broken down, the drilling head cannot be released. Furthermore, if the power unit is stuck, the drilling head is also not released.